Radio communications are widely used in areas including sound signal transmission, video signal transmission, and data transmission. In various radio communication technology areas, radio receivers are used to receive radio waves intercepted by antennas and to convert the information carried by the radio waves into usable forms. Through a demodulation process, a radio receiver converts the information into sound signals, video signals, data, or other useful signals. Devices that contain radio receivers include, e.g., cell phones, wireless network devices, Bluetooth devices, etc.
For industrial, scientific, medical and other purposes, various radio frequency devices transmit and receive radio frequency signals at radio bands, which are collectively labeled the industrial, scientific and medical (ISM) radio bands. Generally, the ISM radio bands are internationally reserved for civil usages. In recent years, these ISM bands have become particularly popular among short-range, low power communications systems. For example, the 2.4 GHz band is used by communications of cordless phones, Bluetooth devices, near field communication (NFC) devices, ZigBee devices, radio control toys, and wireless network devices. Because there are many different usages of the ISM bands, the emissions of the devices operating at the ISM bands can create electromagnetic interferences and disrupt the radio communications of other devices at the same or nearby frequency. Thus, the communication devices operating at the ISM bands need to tolerate the interferences generated by other devices operating at the same or nearby bands.
In addition, there are interferences between wireless local area networks (WLANs). The number of wireless LANs deployed increases every year. Both corporate entities and private families deploy wireless LANs. In some occasions, there is no coordination between the wireless LAN networks during the planning and deployment stages. Therefore, devices within a wireless LAN network can have interferences generated by devices of other wireless LAN networks. The interference problem becomes even more prominent when the network devices have better signal ranges.